1. The Field of the Invention
The present invention is in the field of joint repair surgery, such as reconstruction of the anterior cruciate ligament (ACL). More particularly, the invention is in the field of tensioning devices for conditioning and pre-tensioning sutures attached to soft tissue grafts used in joint repair procedures, such as sutures independently attached to a pair of ham string grafts. The invention is able to independently condition and pre-tension each soft tissue graft individually.
2. The Relevant Technology
Injuries to joints, specifically the knee, are quite common, particularly when one engages in vigorous sporting activities. A common injury is a rupture or tear of the anterior cruciate ligament (ACL), which is the primary ligament responsible for holding the knee joint together and which keeps it from slipping out of joint or dislocating. An unrepaired ruptured or torn ACL can cripple, and would most certainly limit physical activity of, the person suffering a ruptured or torn ACL. Absent reconstruction of the ACL, such injuries would likely be the end of professional sports careers and would prevent ordinary people from enjoying an active life involving sports and like recreation.
Improvements in surgical procedures have made ACL reconstruction procedures more successful and, hence, more common. In general, an ACL reconstruction procedure involves taking a soft tissue graft from another part of the body, such as the patellar tendon or the hamstrings, and attaching it at both ends through a hole drilled through the two bones that make up the knee joint: the femur and the tibia. When secured in place, the soft tissue graft will mimic and, hence, take the place of, the ACL itself. This soft tissue graft holds the femur and tibia together to make the joint more stable, but is flexible enough to allow for normal joint movements (i.e., flexion and extension).
Graft tension in ACL reconstruction has been recognized as an important factor in the clinical outcome of the ACL reconstruction procedure. In other words, grafts that are too loose may be unstable while grafts that are too tight may greatly restrict motion of the knee. Recent interest in graft tension and scientific work on the subject have raised the demand for quality instruments that will assist the surgeon in more effectively fixing ligament grafts under known tension.
Publications in the past few years have emphasized the need for adequate tensioning of the graft. These include Markolf et al., xe2x80x9cBiomechanical Consequences of Replacement of the Anterior Cruciate Ligament With a Patellar Ligament Allograft. Part Two: Forces in the Graft Compared with Forces in the Intact Ligament,xe2x80x9d J. Bone Joint Surg. Am., 78:11, 1728-34 (November 1996); Tohyama et al., xe2x80x9cSignificance of Graft Tension in Anterior Cruciate Ligament Reconstruction. Basic background and clinical outcome,xe2x80x9d Knee Surg. Sports Traumatol. Arthroscopy, 6 Suppl. 1, S30-7 (1998); Andersen et al., xe2x80x9cReview on Tension in the Natural and Reconstructed Anterior Cruciate Ligament,xe2x80x9d Knee Surg. Sports Traumatol. Arthroscopy, 2:4, 192-202 (1994); Yasuda et al., xe2x80x9cEffects of Initial Graft Tension on Clinical Outcome After Anterior Cruciate Ligament Reconstruction. Autogenous Doubled Hamstring Tendons Connected in Series of Polyester Tapes,xe2x80x9d Am. J Sports Med., 25:1, 99-106 (January 1997). For purpose of disclosure, the foregoing publications are incorporated herein by specific reference.
While much of the focus has been directed to the issue of under tensioning, which typically results in knees that are less stable than normal, application of too much tension may in theory also have an adverse effect by constraining the joints or causing increased pressure on articular surfaces.
A recent study by Hamner et al. has added to the understanding of graft tension by demonstrating that unequal tension in the individual strands of the soft tissue graft can result in significant losses in total graft strength and stiffness. Hamner et al., xe2x80x9cHamstring Tendon Grafts for Reconstruction of the Anterior Cruciate Ligament: Biomechanical Evaluation of the Use of Multiple Strands and Tensioning Techniques,xe2x80x9d J. Bone Joint Surg. Am., 81:4, 549-57 (April 1999). Hamner et al. studied whether tensioning the soft tissue strands by hand would result in equalization of the load borne by each strand. Hamner et al. showed that this method was not effective in equalizing the load on the strands, which led to an ultimate graft strength that was not significantly greater than the load of the individual strands taken alone.
Previous work has been done to develop and patent devices that are used to apply a known tension to cruciate ligament grafts. Such devices have typically included simple spring scales that apply a known load to the graft as a whole. E.g., U.S. Pat. No. 4,712,542; U.S. Pat. No. 5,037,426; U.S. Pat. No. Re. 34,762; U.S. Pat. No. 5,713,897; U.S. Pat. No. 5,507,750; and U.S. Pat. No. 5,562,668. For purposes of disclosing mechanisms for applying a known load or tension onto a soft tissue graft, the foregoing patents are incorporated herein by specific reference.
Because none of the foregoing references disclose any method for using these devices to separately tension multiple soft tissue grafts, so as to equalize the stress applied to each, one strand will often be preferentially loaded more than another, thus resulting in disparately conditioned and pre-stressed strands that are not significantly stronger or stiffer than a single strand. More particularly, because hamstrings can have different diameters, simply applying a standard load to both strands simultaneously could result in one graft being subjected to a different material stress than the other graft. Moreover, even in the case of hamstrings or other soft tissue grafts that have the same or substantially the same diameters, inadvertent or unavoidable error by the treating surgeon, such as unequal conditioning of each soft tissue graft, can still lead to uneven loads being borne by each individual graft. Regardless of the causes for unequal application of material stress to each of the individual soft tissue grafts, the xe2x80x9ctighterxe2x80x9d graft (or graft with higher material stress) will reach the failure point first, thereby causing a lower load to failure for the composite graft.
In view of the foregoing, it would be an improvement in the art of joint repair to provide apparatus and methods for independently conditioning and pre-tensioning individual soft tissue graft strands, such as a pair of hamstrings used in an ACL reconstruction procedure.
It would be an additional improvement in the art to provide apparatus and methods for conditioning and pre-tensioning individual graft strands so that each graft strand substantially contributed to the overall strength and stability of the repaired joint.
It would yet be an advancement in the art if such apparatus and methods for conditioning and pre-tensioning individual graft strands could equalize the otherwise unequal conditioning and pre-tensioning of the individual graft strands that might occur, for example, by strands of different diameters or stiffness, or through inadvertent or unavoidable surgical error, such as failure to tie the sutures in a manner so that each graft strand is tensioned equally.
Moreover, it would be an advancement in the art to provide an improved anchor device that could be used in conjunction with such apparatus and methods, which allowed for the independent tensioning of sutures attached to individual soft tissue graft strands, and which could be manipulated after independently tensioning the sutures so as to subsequently lock the sutures in place so as to reliably secure each of the soft tissue graft strands to the bone at a desired tension.
Such apparatus and methods for independently conditioning and pre-tensioning multiple ligament grafts are disclosed and claimed herein.
The present invention encompasses apparatus and methods for independently tensioning a plurality of soft tissue grafts during joint repair procedures, such as in procedures to replace or augment the anterior cruciate ligament (ACL). Because of the importance pre-tensioning soft tissue grafts a predetermined amount, but because of the tendency of soft tissue grafts to relax or stretch after being implanted, it is often necessary to xe2x80x9cconditionxe2x80x9d such grafts prior to anchoring the grafts in place. Soft tissue grafts can be xe2x80x9cconditionedxe2x80x9d by applying a tensile load for a sufficient amount of time order to prevent further stretching or relaxation of the tissue graft over time after being implanted. In addition to conditioning, it is also generally desirable to pre-stress (or pre-tension) the soft tissue grafts in order to ensure a desired degree of joint stability and strength. Thus, both conditioning and pre-tensioning are important procedures which ensure the success of the joint repair surgery.
Grafts are advantageously xe2x80x9cconditionedxe2x80x9d prior to being pre-tensioned in order to take the xe2x80x9cplayxe2x80x9d out of the system. Conditioning assists in tightly seating the graft within the bone tunnel and also assists in fully seating the sutures. Only after all of the play has been taken out of the system can the individual grafts be reliable pre-stressed to a desired degree. Attempting to apply a desired amount of material stress to a graft that has not been adequately conditioned typically results in a decay or diminution of actual material stress born by the graft over time. This may lead to long-term instability of the joint.
A predetermined amount of material stress is advantageously applied to the soft tissue grafts in order to yield a joint having a desired amount of stability and stiffness. Inadequately tensioned soft tissue grafts often yield a joint that is not adequately stable or which is too loose, thus being far more prone to subsequent injury and possible rupture of the tissue grafts. However, unless each strand of a multiple strand graft bears approximately the same magnitude of material stress, the strand that initially bears the highest material stress will reach the failure point and rupture first when the joint is subjected to high stress. Subsequently, the graft initially bearing less material stress will then bear all the stress and be more prone to failure since it will be acting on its own to hold the joint together. In short, a soft tissue graft that includes multiple strands that initially bear differing amounts of material stress results in a joint that is both more elastic and which will have a significantly lower composite load to failure point.
Notwithstanding the important of ensuring that each strand of a multiple strand tissue graft are pre-tensioned so as to bear approximately the same material stress, it has heretofore been very difficult to ensure equal, or substantially equal, conditioning and pre-stressing of each strand. As a result, it has heretofore been difficult to ensure that each of the strands contributes equally and simultaneously to the strength and stiffness of the joint.
The present invention proposes novel apparatus and methods to solve the problems associated with the inability to independently condition and pre-tension each strand of a multiple-strand soft tissue graft. The tensioning devices according to the present invention may be configured to apply a desired amount of tension or load to single- or multi-stranded grafts. In a preferred embodiment, the inventive apparatus comprises a tensioning device that includes a plurality of separate adjustable tension applicators (e.g., two) capable of independently applying a desired level of tension to each of the plurality (e.g., two) of soft tissue grafts used in the joint repair surgery. The tensioning device further includes attachment means for removably attaching the device to a patient""s bone or limb during the surgical procedure.
An advantage of the inventive tensioning device is the ability to pre-condition the graft after implantation at one end but before fixation. In the case of an ACL reconstruction procedure, because the graft is attached to the tibia near the fixation site, the graft can be tensioned and conditioned by repeatedly flexing and extending the patient""s knee under load to remove any laxity or looseness in the graft construct.
The proposed device is advantageously free-standing on the tibia, which can free the surgeon""s hands to set knee flexation angle and fix the distal end of the graft while monitoring tension. The device will also be able to sustain a load on the graft for static loading that will help stretch the graft before fixation.
In one embodiment, each adjustable tension applicator of the tensioning device includes attachment means for securing one or more sutures attached to the soft tissue graft and an adjustable biasing mechanism (e.g., a spring-loaded mechanism) capable of applying a measured tensile load to the sutures and associated soft tissue graft. The adjustable biasing mechanism further includes an immobile base or block, a cylinder block or module slidably disposed on the immobile base, a tensioning piston slidably disposed within a portion of the cylinder block, a biasing spring communicating between the cylinder block and the tensioning piston, and a rotatable adjustment knob threadably attached to the slidable cylinder block, which, upon turning, selectively urges the cylinder block towards or away from the tensioning piston so as to selectively compress or extend the biasing spring and thereby increase or decrease the load applied by the biasing spring onto the tensioning piston.
The means for securing the one or more sutures to the tensioning pistons may advantageously include a suture attachment wheel rotatably connected to each tensioning piston. Free rotation of the suture attachment wheel ensures equal tension being applied to each side of a looped suture strand.
While the tensioning device is in use, outward movement of the tensioning piston relative to the slidable cylinder block as the compressive force applied by the biasing spring is restricted by the countervailing inward tension exerted by the soft tissue graft attached to the tensioning piston by means of the sutures. Thus, during conditioning and subsequent pre-tensioning of the soft tissue graft, the tensioning piston may only move a few millimeters, or less, as the soft tissue graft is stretched. Turning of the adjustment knob causes the slidable cylinder block to move either towards or away from the essentially immobilized tensioning piston. Movement of the cylinder block towards the tensioning piston causes the biasing spring to become progressively compressed, thus increasing the outward, or compressive, force exerted by the spring onto the piston. Likewise, movement of the cylinder block away from the piston progressively decompresses the biasing spring, thus decreasing the compressive force exerted by the spring onto the piston.
The magnitude of compressive force exerted by the biasing spring onto the piston is essentially equivalent to the magnitude of the tensile force exerted onto the soft tissue graft by the tensioning piston. Because the amount of compressive force exerted by a spring is directly related to the distance that the spring has been compressed, the compressive load exerted by the spring onto the tensioning piston, and the tensile load exerted by the tensioning piston onto the soft tissue graft, can be indirectly measured by measuring the distance the spring has been compressed. Thus, the adjustable biasing mechanism may advantageously be equipped with a gauge or other means for measuring the magnitude of spring compression so as to indirectly measure the amount of tensile load being exerted on the soft tissue graft during conditioning and pre-tensioning.
Notwithstanding the foregoing, one will readily appreciate, in view of the disclosure herein, that inventive devices according to the invention are not limited to any particular mechanism for performing the individual and separate tasks of independently tensioning a plurality of strands of a soft tissue graft. The mechanisms described herein are but illustrative and exemplary. For example, the tension loading function could alternatively be provided by a variety of simple scales, such as tension springs, compression springs, torsion springs or electronic transducers. In addition a variety of electronically actuated and measured tensioning devices are certainly within the scope of the invention so long as they are capable of independently tensioning separate soft tissue grafts. Examples include a strain gauge, a rotary guage, an LVDT and the like.
The tensioning device can potentially be used to monitor isometry and measure tension in a single strand of a soft tissue graft. The current design could also be altered in order to incorporate additional adjustable tension applicators that can exert and measure tension in as many stands as a surgeon might choose to include in the soft tissue graft.
In a preferred method for carrying out the procedures according to the present invention, two soft tissue grafts are taken from the patient, such as from the ham strings or patellar tendon, drawn through holes bored through the femur and tibia according to known surgical procedures, and attached to the femur according to known surgical procedures. Sutures are attached to the strands of the soft tissue graft at an appropriate point during the implantation procedure using known methods. The end of the soft tissue graft opposite the sutures is passed through holes bored through the tibia and femur and secured to the femur using known surgical procedures. The sutures and a portion of the graft extend out of an access hole in the patient""s leg near the hole in the tibia.
Thereafter a tensioning device capable of separately applying a tension to each of the soft tissue grafts is provided, an example of which is the preferred device described more fully herein. The tensioning device will advantageously include two or more adjustable tension applicators corresponding to the two or more soft tissue graft strands, respectively. The tensioning device is then attached to the patient""s bone or limb by means of guide pins drilled into the bone, or some other appropriate manner (i.e., by means of a belt or band wrapped around the patient""s leg), followed by attaching the sutures associated with one of the soft tissue graft strands to one adjustable tension applicator and attaching the other soft tissue strand to the other adjustable tension applicator. In the case of a modular tensioning device, the module responsible for securing the tensioning device to the patient""s tibia is advantageously attached to the leg first. Thereafter, the module responsible for applying the tensile load to the soft tissue grafts is attached to the attachment module. Of course, a single, non-modular unit may also be employed.
After the sutures have been secured to the tensioning device, the tensioning device is used to independently apply a desired tensile load to each of the two soft tissue graft strands. This may be done, for example, by tightening the tension knobs of each adjustable tension applicator described above so as to compress the biasing spring and thereby apply a corresponding compressing force onto each tensioning piston, which is essentially equal to the magnitude of the tensile load exerted by the tensioning piston onto the soft tissue graft strand.
Thereafter, the joint (e.g., the knee) is advantageously xe2x80x9ccycledxe2x80x9d by the treating physician, i.e., flexed and extended between zero and 90xc2x0 a number of times (e.g., 25 repetitions) in order to assist in conditioning the soft tissue graft strands and also to test the joint stability. The process of increasing the tensile load applied to each of the soft tissue graft strands by the tensioning device followed by cycling of the joint is repeated until a desired level of conditioning, prestressing and associated joint stability and strength are achieved. When negligible losses in joint stability are observed, the soft tissue graft is secured to the bone (e.g., the tibia) by appropriate anchoring means known in the art, or by means of the novel implantable anchor device disclosed herein.
An example of anchoring means known in the art is an interference screw, which is screwed directly into the hole in the patient""s bone (e.g., the tibia) through which the soft tissue graft is passed by means of a driver. After the interference screw has been screwed in place, the driver and tensioning device are removed. If guide pins are used to secure the tensioning device to the person""s leg, these are also removed. The remaining portion of the soft tissue grafts that extend beyond the bone may be secured to the outer surface of the bone by securing means known in the art, e.g., a spiked washer, staple or post in order to reinforce fixation of the graft. The graft is then trimmed to remove the sutures, and the incision in the leg closed.
In an alternative embodiment, a novel implantable anchor device may be employed to secure the soft tissue graft to the tibia or other bone. An exemplary anchor includes a cylindrical outer sheath having a cylindrical outer wall and a generally cylindrical bore therethrough, and a corresponding locking core or shaft used to lock the sutures into place once the conditioning and pre-tensioning procedure has been completed. The circumference of the outer sheath is selected to fit within the hole bored through the tibia or other bone.
The bottom part of the outer sheath, or the part of the sheath which faces the bone, includes a plurality of suture holes disposed near the outer edge of the sheath adjacent to the cylindrical outer wall. The suture hole permits passage therethrough of the individual strands of the sutures attached to the soft tissue grafts. The outer sheath, inward of the suture holes, may be closed or include a hole through center of the sheath bottom face. A hole permits the passage therethrough of an interference screw, post, or other device capable of urging the soft tissue graft against the walls of the hole through the bone to promote faster adhesion thereto. The use of an interference screw also strengthens the fixation of the graft to the bone.
The top part of the sheath, or the part of the sheath facing away from the bone, includes a lip or other protrusion extending laterally from the edge of cylindrical outer wall. When the anchor device is placed into the bore within the tibia or other bone, the lip or other protrusion advantageously overlaps the outer surface of the bone, thus acting as a stop to hold the anchor device in a desired location. The inward tension exerted by the soft tissue graft onto the sutures effectively pulls the lip or protrusion against the bone, thus reliably locking the anchor device against the bone.
The locking core is capable of sliding into and out of the outer sheath, but has a slightly tapered outer wall so that it can form an increasingly tighter press fit with the inner wall of the outer sheath as it is pressed or forced into the sheath. The locking core is preferably hollow and includes suture passages passing through the bottom edge nearest, and corresponding to, the suture holes of the outer sheath. The suture passages pass approximately longitudinally through the locking core but at an angle so that they exit through the outer wall of the locking core rather than the top edge, or the edge facing away from the outer sheath. In this way, the sutures will pass through the locking core in a manner so that, when the locking core is deployed, the sutures will be tightly pinched between the outer wall of the locking core and the inner wall of the outer sheath. This pinching action prevents the sutures from slipping back into the bone hole, thus maintaining the desired tension on the sutures and associated soft tissue graft strands after conditioning and pre-tensioning of the individual graft strands, as described more fully herein. Prior to deployment of the locking core, the sutures are free to slide inwardly or outwardly as desired relative to the outer sheath and the locking core, which allows the tensioning device to increase or decrease the tensile load applied to the soft tissue graft strands, as desired.
Accordingly, it is an object of the invention to provide apparatus and methods for independently conditioning and pre-tensioning individual soft tissue graft strands, such as a pair of hamstrings used in an ACL reconstruction procedure.
It is an additional object and feature of the invention to provide apparatus and methods for conditioning and pre-tensioning individual graft strands so that each graft strand may substantially contribute to the overall strength and stability of the repaired joint.
It is yet an object of the invention to provide apparatus and methods for conditioning and pre-tensioning individual graft strands that can equalize the otherwise unequal conditioning and pre-tensioning of the individual graft strands that might occur, for example, by strands of different diameters or stiffnesses, or through inadvertent or unavoidable surgical error, such as failure to tie the sutures in a manner so that each graft strand is tensioned equally.
Moreover, it is an object to provide an improved anchor device that can be used in conjunction with the foregoing apparatus and methods, which allows for the independent tensioning of sutures attached to individual soft tissue graft strands, and which can be manipulated after independently tensioning the sutures so as to subsequently lock the sutures in place and thereby reliably secure each of the soft tissue graft strands to the bone at a desired tension.
These and other objects and features of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter.